1. Volcanoes

2. What are volcanoes?
A volcano is an opening in Earth that erupts gases, ash, and lava.

3. How do volcanoes form?
Magma is less dense than the rock around it, so it is forced toward the surface
Vent: Opening that magma flows through
Crater: The steep-walled depression around a volcano’s vent

4. Where do volcanoes occur?
Divergent Plate Boundaries
Iceland
Mid-Atlantic Ridge
Convergent Plate Boundaries
Oceanic Plate slides beneath Continental Plate
Andes mountains in South America
Erupt more violently
Oceanic Plate slides beneath Oceanic Plate

5. Where do volcanoes occur?

6. Where do volcanoes occur?
Hot Spots
Areas between Earth’s mantle and core that are unusually hot.
Hot rock forces toward the crust where it melts partially to form a hot spot.
Hawaiian Islands
Pacific Plate moving over a stationary hot spot.

7. Hot Spot Occurrence

8. What controls eruptions?
Trapped Gases
Composition of Magma
Silica Poor
Silica Rich
Varying Silica Content

9. Liquid Hot Magma!!!!

10. What controls eruptions?
Silica Poor: quiet eruption
Basaltic Magma, Pahoehoe flows
Silica Rich: explosive eruption
Granitic Magma, Mount St. Helens, WA
Intermediate Silica: Quiet / explosive eruption.
Andesitic Magma, Convergent Plate Boundaries, Krakatau, South America

11. Forms of Volcanoes Shield Volcano
Quiet eruptions of basaltic lava spread out in flat layers
Layers buildup and form a broad volcano with gently sloping sides
Hawaiian Islands

12. Forms of Volcanoes Cinder Cone Volcanoes
Explosive eruptions throw lava and rock high into the air
When rock and ash land, it forms a steep-sided, loosely packed volcano
Paricutín, Mexico

13. Forms of Volcanoes Composite Volcano
Varying explosions depend on amount of silica and trapped gases.
Alternating layers of lava and ash form a volcano
Mount Rainier, WA

14. Violent Eruptions 1883: Krakatau, Indonesia 1906: Vesuvius, Italy
1983: Kilauea, Hawaii
2000: Popocatepetl, Mexico

15. Volcanic Activity Reports